Melania Geymonat, 28, and her date Christine Hannigan were pelted with coins on a Camden night bus on 30 May.
The teenagers, aged 15, 16 and 17, had previously denied charges of harassment by using threatening or abusive words or behaviour.
They admitted the public order offences ahead of a scheduled trial at Highbury Corner Youth Court.
The 17-year-old will appear in court on Friday for a Newton hearing, to decide whether an aggravating factor of homophobia should be considered on sentencing.
All three boys will be sentenced at the same court on 23 December.
Prosecutor Saira Khan said the teenagers each played different roles in the nine-minute incident.
Ms Geymonat and Ms Hannigan were initially sitting alone on the top deck of the N31 bus when they were approached by the group of boys.
The women were surrounded and sexual gestures were made by the teenagers.
CCTV showed a fight breaking out on the bus, with both Ms Geymonat and Ms Hannigan being punched several times.
The suspects also left with a phone and a bag.
It was alleged the boys threw coins at the women, who were both taken to hospital for treatment to facial injuries.
In addition to the public order offences, a 16-year-old boy also pleaded guilty to handling a stolen mobile phone while a 15-year-old boy admitted handling a stolen bank card.
Judge Susan Williams said the abuse “was quite clearly directed towards this couple because of who they are”.
Transport for London’s Mandy McGregor said after the hearing: “This sickening incident was utterly unacceptable. Homophobic abuse is a hate crime and won’t be tolerated on our network.”
Police said charges were dropped against another 17-year-old boy.
Speaking after the attack in May, Ms Hannigan told the BBC she was “not scared to be visibly queer”.
“If anything, you should do it more,” she added.
Ms Geymonat, who is a qualified doctor but works for Ryanair as a flight attendant, said she agreed.
Ms Hannigan said: “I was and still am angry. It was scary, but this is not a novel situation.”
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